Porsche has increased its 5% stake in Volkswagen to 10.3% as it moves to acquire 20% of the company.

Immo Dehnert, a spokesman for the Stuttgart-based sportscar maker, said the shares Porsche had purchased so far had been from institutional investors, but added that the company was looking at other sources to increase its stake in VW.

It is widely assumed Porsche is taking this step to help prevent a hostile takeover of VW.

Porsche said the move was based on the close relationship between the two carmakers in development and manufacturing, describing Volkswagen as "not only an important development partner but also a significant supplier for about 30% of sales volume" for Porsche.

"The stake will in no case reach the level at which Porsche would have to make a public offer to take over VW," Porsche said.